The purpose of the proposed project is to compare the efficacy of two fully developed physical therapy interventions in 8-24 months olds with or at high risk of having Cerebral Palsy (CP). Sitting Together And Reaching To Play (START-Play) targets sitting, reaching and motor-based problem solving in infancy to improve global development. Usual Care Physical Therapy (UCPT) focuses on advancing motor skills and preventing impairments. The project builds on a nearly complete clinical trial evaluating the efficacy of the START-Play intervention compared to a non-dose matched comparison group. The proposed study directly addressed the need for a dose-matched clinical trial to consider the impact of dose of intervention on efficacy. A direct comparison of START-Play with the dose matched (24 visits in 3 months) UCPT provided in the same environment (homes) and provided by licensed physical therapists will allow for a direct comparison of the efficacy of interventions based on two different set of key principles. START-Play is based on developmental and basic science, motor learning, and neuroplasticity, in addition to our extensive preliminary efficacy data. START-Play has been fully described with a protocol manual, training documents, and fidelity measures. The UCPT intervention is based on videotaped session of the comparison group community based intervention sessions and parent report for the ongoing clinical trial. A fidelity measure used the previous research quantifies differences in the focus of these interventions and will be used to maintain adherence to both intervention groups. Three sites in different regions of the United States will recruit from local intervention and medical centers for a total of 150 infants with or at high risk of having cerebral palsy between ages 4-24 months of age, when they show readiness skills for early sitting and reaching. Risk for CP will be based on the early detection guidelines and all outcome measures are included in the NIH supported Common Data Elements for Cerebral Palsy. Each infant will be randomized into a group and will receive the START-Play or the UCPT intervention for 3 months, with follow up extending for 12 months from baseline. The primary objectives examine change over time in sitting gross motor and cognitive development. Differences in outcomes between the two intervention groups will be examined. In addition, we will begin to identify predictors of response to developmental motor interventions by evaluating the relationship between intervention outcomes and 1) infant and family characteristics, 2) presence of white matter, cerebellar, basal ganglion, or gray matter injury.